The invention discloses a GIS partial discharge external sensor which comprises a microstrip antenna. The microstrip antenna comprises: a metal ground plate which has an upper surface and a lower surface; a medium substrate which has an upper surface and a lower surface, wherein the lower surface of the medium substrate is in contact with the upper surface of the ground plate; and a metal paster which has an upper surface and a lower surface, wherein the lower surface of the metal paster is in contact with the upper surface of the medium substrate. A radio frequency electromagnetic field is formed between the metal paster and the ground plate, and a direction of the radio frequency electromagnetic field is perpendicular to a plane which the ground plate locates at and points at the ground plate from the metal paster.